Drok Meter Electric Box Cover Mounting Plate

I needed a way to mount one of the Drok AC Volt/Amp meters (such as this one: https://www.amazon.com/DROK-80-300V-Voltmeter-Multimeter-Transformer/dp/B01MRZAFAF/) for my Musical Tesla Coil and decided the best way was to use an off-the-shelf electric box as I was already using for its power switch and outlet. So I fired up OpenSCAD and made this.

I added an adjustable "spacer" thickness for the plate, as my box had a hump in the back for a ground connection and so the meter needed a little c